In a powder coating system, a powder, such as a resinous polymer in the form of powder particles, is initially adhered to the exposed surface of an article to form a powder coating on the article. This initial coating process typically involves electrically grounding the article being coated and electrostatically charging the powder particles such that an electrostatic attraction causes the powder to adhere to the article in a substantially uniform thickness. The coated article is then cured using heat to fully adhere the coating to the article.
In one known technique for adhering powder particles to articles, a fluidized bed of electrostatically charged powder particles is formed for supplying the powder particles to the articles. A layer of the powder particles is aerated by means of ionized air passing upwardly through a porous surface, i.e., a porous plate or a screen, supporting the powder particles. The particles generally all carry the same charge and repel each other to form a cloud of substantially uniformly distributed charged particles. Grounded articles located in the area of the cloud of charged particles attract the charged particles to form a coating on the grounded articles. The particles are generally more attracted to areas that are uncoated than those areas that already have a coating, such that a generally uniform coating of the particles is formed on the exposed surfaces of the article.
Typically, it is desirable to coat certain portions of an article surface while leaving remaining surfaces on the article uncoated prior to the curing step of the process. Further, when coating surfaces on the interior of an article, it is advantageous to provide a certain flow of particles onto the article to ensure that a sufficient density of particles will pass into contact with all surfaces to be coated. For example, a stator stack for a dynamo-electric machine requires that a coating be provided to slot portions and end surfaces of the stator stack that contact stator windings, while leaving remaining surfaces uncoated The stator slots comprise elongated passages of relatively small cross section which may not receive sufficient flow from the aerated cloud of particles to form a coating of the desired uniformity. An example of a stator stack that may receive a coating is illustrated in U.S. Pat. No. 5,964,429, which patent is incorporated herein by reference.
An additional aspect associated with powder coating comprises containing the powder to limit dispersal of the powder to the surrounding environment. In particular, the powder comprises very fine particulate material that has typically required operations to be performed in chambers or enclosures in order to ensure containment of the powder. However, known production configurations incorporating enclosures present a limitation to effective production processes, including those incorporating automated processing of articles.
Accordingly, there is a need for a method and/or system for coating stator stacks with a powder coating that provides a uniform thickness, and that may be performed in a consistent and efficient manner. There is a further need for a method and/or system to efficiently process stator stacks with a coating material, where portions of the stator stacks may be coated and remaining portions are without the coating material.